This is exactly why I returned to the iOS. I just can't go without iMessage. I really found nothing on the Android side that compared. I have been using the iPhone since the iPhone 3G. I decided to give Android a try with the Nexus 6P. Wonderful phone but I hated using SMS text in comparison to iMessage. Other Android apps didn't really seem to fit the void I felt by the lost of iMessage. After two weeks, I came right back to the iPhone 7 Plus.
But the thing is, iMessage is proprietary. So even if Android did have an iMessage equivalent, when you message iPhone users, you'll still be under regular SMS restrictions or you'll have to get them to install that Google message app on the iPhone.
This is why I don't understand half the arguments made about the need of iMessage, it's never going to be compatible with anything but iPhones. I completely understand the criticism of Android's default message app only being a SMS client, and yes, Android needs to get with the times in that regard. But iPhone users need to realize, once you leave iPhone, your iMessage privileges are gone when messaging other iPhones users, unless you get them to install and use something other than the default iMessage. And that seems to be the biggest criticism of iPhone users against Android, which makes no sense.
Being that said ... When messaging cross platform beyond standard SMS rules. One party or the other has no choice but to use a 3rd party app, being that iMessage is the proprietary default for iOS. So the argument of the sender or receiver's need to install a 3rd party app being a hassle is void. It's not a hassle, it's a must. And completely on Apple.
Now when a user mostly communicates with other iPhone users, if iMessage is that important to them, then stick to iPhones. Cause it will be an unavoidable problem otherwise.